Solubility of Hydrothermally Altered Volcanic Rocks in Acid Solutions

Abstract

Rock matrix stimulation has been a methodology used to enhance well productivity in oil systems. Some years ago this methodology began to be applied in geothermal systems. In order to investigate the behavior of altered volcanic rocks interacting with an acid solution, experiments were carried out using mostly volcanic altered rocks from geothermal reservoirs. The common acid solutions used during acid well stimulation, 10% HCl and a mixture of 10 % HCL-5 % HF, were used to investigate solubility of rock. Experiments were conducted at atmospheric pressure and temperature of 110 ± 5°C. The chemistry, the mineralogy and the permeability of selected rocks were determined before and after the reaction with each acid solution. Mineral dissolution depends on the type and the intensity of hydrothermal alteration of rocks. As it is expected Calcite readily reacts with acids leaving empty veins and micro fractures (worm holes). Calc- silicates are resistant to acid solutions; partial dissolution of minerals is noted in the external surfaces of the specimen in contact with the acid solution leaving the rock matrix unreacted.